Optical analysis system

ABSTRACT

An optical analysis system ( 1 ), which is arranged to determine amplitude of a principal component of an optical signal, includes a first detector ( 5 ) for detecting the optical signal weighted by a first spectral weighting function, and a second detector ( 6 ) for detecting the optical signal weighted by a second spectral weighting function. For an improved signal-to-noise ratio, the optical analysis system ( 1 ) further includes a dispersive element ( 2 ) for spectrally dispersing the optical signal, and a distribution element ( 4 ) for receiving the spectrally dispersed optical signal and for distributing a first part of the optical signal weighted by the first spectral weighting function to the first detector ( 5 ) and a second part of the optical signal weighted by the second spectral weighting function to the second detector ( 6 ). The optical analysis system ( 1 ) is suited for use in numerous applications including a spectroscopic analysis system ( 30 ) and a blood analysis system ( 40 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC § 371 National Stage application of PCTApplication PCT/l03/05467 filed Nov. 21, 2003, which claims the benefitunder 35 USC § 119(a) of European Patent Office (EPO) Application No.02080427.4 filed Dec. 19, 2002.

BACKGROUND

The invention relates to an optical analysis system for determining anamplitude of a principal component of an optical signal, the opticalanalysis system comprising a first detector for detecting the opticalsignal weighted by a first spectral weighting function, and a seconddetector for detecting the optical signal weighted by a second spectralweighting function.

The invention also relates to a spectroscopic analysis system comprisingsuch an optical analysis system.

The invention also relates to a blood analysis system comprising such anoptical analysis system.

U.S. Pat. No. -B1-6,198,531 discloses an embodiment of an opticalanalysis system described in the opening paragraph.

The known optical analysis system is part of a spectroscopic analysissystem suited for, e.g., analyzing which compounds are comprised atwhich concentrations in a sample. It is well known that lightinteracting with the sample carries away information about the compoundsand their concentrations. The underlying physical processes areexploited in optical spectroscopic techniques in which light of a lightsource such as, e.g., a laser, a lamp or light-emitting diode isdirected to the sample for generating an optical signal which carriesthis information.

For example, light may be absorbed by the sample. Alternatively or inaddition, light of a known wavelength may interact with the sample andthereby generate light at a different wavelength due to, e.g., a Ramanprocess. The transmitted and/or generated light then constitutes theoptical signal which may also be referred to as the spectrum. Therelative intensity of the optical signal as function of the wavelengthis then indicative of the compounds comprised in the sample and theirconcentrations.

The optical signal has to be analyzed so as to identify the compoundscomprised in the sample and to determine their concentrations. In theknown optical analysis system the optical signal is analyzed bydedicated hardware comprising an optical filter. This optical filter hasa transmission which depends on the wavelength, i.e. it is designed toweigh the optical signal by a spectral weighting function which is givenby the wavelength dependent transmission. The spectral weightingfunction is chosen such that the total intensity of the weighted opticalsignal, i.e. of the light transmitted by the filter, is directlyproportional to the concentration of a particular compound. Thisintensity can then be conveniently detected by a detector such as, e.g.,a photo-diode. For every compound a dedicated optical filter with acharacteristic spectral weighting function is used. The optical filtermay be, e.g., an interference filter having a transmission constitutingthe desired weighting function.

For successful implementation of this analysis scheme it is essential toknow the spectral weighting functions. They may be obtained, e.g., byperforming a principal component analysis of a set comprising N spectraof N pure compounds of known concentration where N is an integer. Eachspectrum comprises the intensity of the corresponding optical signal atM different wavelengths, where M is an integer as well. Typically, M ismuch larger than N. Each spectrum containing M intensities atcorresponding M wavelengths constitutes an M-dimensional vector whose Mcomponents are these intensities. These vectors are subjected to alinear-algebraic process known as singular value decomposition (SVD)which is the core of principal component analysis and is well understoodin this art.

As a result of the SVD a set of N eigenvectors z_(n), with n being apositive integer smaller than N+1, is obtained. The eigenvectors z_(n)are linear combinations of the original N spectra and often referred toas principal components or principal component vectors. Typically, theprincipal components are mutually orthogonal and determined asnormalized vectors with |z_(n)↑=1. Using the principal components z_(n),the optical signal of a sample comprising the compounds of unknownconcentration may be described by the combination of the normalizedprincipal components multiplied by the appropriate scalar multipliers:x₁z₁+x₂z₂+ . . . +x_(n)z_(n),

The scalar multipliers X_(n), with n being a positive integer smallerthan N+1, may be considered as the amplitudes of the principalcomponents z_(n) in a given optical signal. Each multiplier x_(n) can bedetermined by treating the optical signal as a vector in the Mdimensional wavelength space and calculating the direct product of thisvector with a principal component vector z_(n). This yields theamplitude x_(n) of the optical signal in the direction of the normalizedeigenvector z_(n). The amplitudes x_(n) correspond to the concentrationsof the N compounds.

In the known optical analysis system the calculation of the directproduct of the vector representing the optical signal and theeigenvector representing the principal component is implemented in thehardware of the optical analysis system by means of the optical filter.The optical filter has a transmittance such that it weighs the opticalsignal according to the components of the eigenvector representing theprincipal component, i.e. the principal component vector constitutes thespectral weighting function. The filtered optical signal can be detectedby a detector which generates a signal with an amplitude proportional tothe amplitude of the principal component and hence to the concentrationof the corresponding compound.

In a physical sense, each principal component is a constructed“spectrum” with a shape in a wavelength range within the optical signal.In contrast to a real spectrum, a principal component may comprise apositive part in a first spectral range and a negative part in a secondspectral range. In this case the vector representing this principalcomponent has positive components for the wavelengths corresponding tothe first spectral range and negative components for the wavelengthscorresponding to the second spectral range.

An embodiment of the known optical analysis system is designed toperform the calculation of the direct product of the vector representingthe optical signal and the eigenvector representing the principalcomponent in the hardware in cases where the principal componentcomprises a positive part and a negative part. To this end, a part ofthe optical signal is directed to a first filter which weighs theoptical signal by a first spectral weighting function corresponding tothe positive part of the principal component, and a further part of theoptical signal is directed to a second filter which weighs the opticalsignal by a second spectral weighting function corresponding to thenegative part of the principal component. The light transmitted by thefirst filter and by the second filter is detected by a first detectorand a second detector, respectively. The signal of the second detectoris then subtracted from the signal of the first detector, resulting in asignal with an amplitude corresponding to the concentration.

In another embodiment the known optical analysis system is able todetermine the concentrations of a first compound and of a secondcompound by measuring the amplitudes of a corresponding first principalcomponent and of a second principal component. To this end, a part ofthe optical signal is directed to a first filter which weighs theoptical signal by a first spectral weighting function corresponding tothe first principal component, and a further part of the optical signalis directed to a second filter which weighs the optical signal by asecond spectral weighting function corresponding to the second principalcomponent. The light transmitted by the first filter and by the secondfilter is detected by a first detector and a second detector,respectively. The signals of the first detector and the second detectorcorrespond to the amplitudes of the first principal component and of thesecond principal component, respectively.

It is a disadvantage of the known optical analysis system that thesignal-to-noise ratio is relatively low.

SUMMARY

It is an object of the invention to provide an optical analysis systemof the kind described in the opening paragraph, which is capable ofproviding a signal with a relatively high signal-to-noise ratio.

The invention is defined by the independent claims. The dependent claimsdefine advantageous embodiments.

According to the invention the object is realized in that the opticalanalysis system further comprises a dispersive element for spectrallydispersing the optical signal, and a distribution element for receivingthe spectrally dispersed optical signal and for distributing a firstpart of the optical signal, weighted by the first spectral weightingfunction, to the first detector and a second part of the optical signal,weighted by the second spectral weighting function, to the seconddetector.

The invention is based on the insight that the signal to noise ratio isrelatively low in the known optical analysis system, because asignificant part of the optical signal is not detected by any of thedetectors, but blocked by, e.g., the first optical filter or the secondoptical filter. For instance, the optical signal received by the firstoptical filter comprises all information but the first filter transmitsonly the part of the optical signal corresponding to the first weightingfunction whereas the part of the optical signal corresponding to thesecond weighting function is blocked by the filter. The light blocked bythe first optical filter and the second optical filter is not detected,leading to a reduced signal-to-noise ratio.

According to the invention this reduction of the signal-to-noise ratiois at least partly avoided. To this end, the optical analysis systemcomprises a dispersive element such as, e.g., a grating or a prism forspectrally dispersing the optical signal. The spectrally dispersedoptical signal is received by a distribution element, i.e. differentparts of the distribution element receive different wavelengths of theoptical signal. For individual wavelengths the distribution element isarranged to distribute a first part of the optical signal, weightedaccording to the first spectral weighting function, to the firstdetector and a second part of the optical signal, weighted according tothe second spectral weighting function, to the second detector. Thus,instead of partly blocking the optical signal as is done by the firstoptical filter and the second optical filter of the known opticalanalysis system, the different parts of the optical signal are directedto different detectors. As a consequence a larger amount of the opticalsignal is detected, yielding an improved signal-to-noise ratio.

According to the invention the optical signal is not restricted tooptical signals having wavelengths which are visible to the human eye.The optical signal may comprise spectral components in the ultraviolet(UV) and/or in the infrared (IR) spectral range. Here, the IR spectralrange may comprise the near infrared (NIR) and the far infrared (FIR)which has a frequency above 1 THz, and all intermediate wavelengths aswell.

According to the invention the principal component is not limited to apure principal component. Here, a pure principal component refers to amathematically exact eigenvector for a certain compound. A principalcomponent may also comprise minor contributions from other compoundswhich may result from imperfections in the determination of theprincipal components. A principal component may also correspond to amixture of several compounds of known concentration.

In an embodiment the principal component comprises a positive part in afirst spectral range and a negative part in a second spectral range, thefirst part of the optical signal weighted by the first spectralweighting function corresponding to the positive part, the second partof the optical signal weighted by the second spectral weighting functioncorresponding to the negative part, the first detector and the seconddetector being coupled to a signal processor arranged to subtract asignal generated by the second detector from a signal generated by thefirst detector. In this embodiment an optical signal comprising aprincipal component having a positive part and a negative part can beanalyzed with an improved signal-to-noise ratio. Typically, the firstspectral range is free from the second spectral range.

In another embodiment the principal component comprises a firstprincipal component and a second principal component, the first part ofthe optical signal weighted by the first spectral weighting functioncorresponding to the first principal component, the second part of theoptical signal weighted by the second spectral weighting functioncorresponding to the second principal component. This optical analysissystem is particularly suited for analyzing samples comprising two ormore compounds each having a corresponding principal component. Itprovides the concentrations of the two or more compounds with animproved signal-to-noise ratio.

In yet another embodiment the principal component comprises a firstprincipal component and a second principal component, and the firstprincipal component and/or the second principal component comprises apositive part in a first spectral range and a negative part in a secondspectral range.

It is advantageous if the distribution element has a surface forreceiving the spectrally dispersed optical signal, the surfacecomprising a first set of surface elements and a second set of surfaceelements, the surface elements of the first set being arranged todistribute the spectrally dispersed optical signal to the firstdetector, the surface elements of the second set being arranged todistribute the spectrally dispersed optical signal to the seconddetector. In this embodiment, each surface element receives, independence on its position and its surface area, a certain portion ofthe spectrally dispersed optical signal. The first weighting function isthen determined by the positions and the surface areas of the surfaceelements of the first set, and the second weighting function isdetermined by the positions and the surface areas of the surfaceelements of the second set. The spectrally dispersed optical signalreceived by the surface may be reflected and/or diffracted by thesurface. Alternatively, it may be transmitted and refracted and/ordiffracted.

This embodiment has the advantage that the distribution element can bemanufactured relatively easily by, e.g., using a transparent substratesuch as a glass substrate which is provided with surface elements byetching and/or polishing. Alternatively, the substrate may bemanufactured using an appropriately shaped mold. An additional advantageof a transparent substrate is that the optical signal loss is relativelylow.

In another embodiment the distribution element comprises an array ofliquid crystal cells arranged to form a first set of sub-arrays havingrefractive index gradients, and a second set of sub-arrays havingrefractive index gradients, the sub-arrays of the first set beingarranged to distribute the spectrally dispersed optical signal to thefirst detector, the sub-arrays of the second set being arranged todistribute the spectrally dispersed optical signal to the seconddetector.

The index of refraction of the cell is controlled by applying a voltageto a cell of the liquid crystal array. A sub-array of cells with arefractive index gradient is created by applying different voltages toneighboring cells. The gradient can be adjusted by adjusting thevoltages. The spectrally dispersed optical signal is refracted by therefractive index gradients of the sub-arrays. The sub-arrays of thefirst set refract the optical signal to the first detector, and thesub-arrays of the second set refract the optical signal to the seconddetector. In this embodiment, analogously to the embodiment describedabove, each sub-array receives, in dependence on its position, a certainspectral portion of the spectrally dispersed optical signal. The firstweighting function is then determined by the positions and the surfaceareas of the sub-arrays of the first set, and the second weightingfunction is determined by the positions and the surface areas of thesub-arrays of the second set.

This embodiment has the advantage that the first spectral weightingfunction and the second spectral weighting function can be adjustedrelatively easily by adjusting the voltages applied to the cells of theliquid crystal array. This is particularly useful because the samedistribution element can be used to analyze optical signals comprisingdifferent principal components.

It is advantageous if the dispersive element is arranged to disperse theoptical signal in a dispersive plane and the optical analysis systemfurther comprises a focusing member for focusing the dispersed opticalsignal, the focusing member having a first focal distance in thedispersive plane and a second focal distance in a plane perpendicular tothe dispersive plane, the first focal distance being different from thesecond focal distance. In this embodiment the spectrally dispersedoptical signal is focused on the distribution element such that thedifferent spectral components of the optical signal are received bydifferent portions of the distribution element. It is then possible toselectively distribute different wavelengths to different detectors. Itis advantageous if the focusing member is arranged to focus thedispersed optical signal in the dispersive plane on the distributionelement.

In this embodiment it is also advantageous if the optical analysissystem further comprises a further focusing member for focusing thefirst part of the optical signal on the first detector. This allows theuse of a first detector having a relatively small detection area forefficiently detecting the first part.

For an efficient detection using detectors with an even smallerdetection area it is advantageous if the optical analysis system furthercomprises a further dispersive element for spectrally recombining thefirst part of the optical signal prior to focusing the first part on thefirst detector. The first part of the optical signal distributed by thedistribution element is in principle still spectrally dispersed, thuslimiting the possibility to focus the first part to a small detectionarea. By using a further dispersive element, the first part of theoptical signal is spectrally recombined which allows for focusing it toa smaller area. Therefore, a smaller first detector placed in this focuscan be used. Alternatively, a pinhole or aperture may be placed in thisfocus to implement a confocal detection scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the optical analysis system, thespectroscopic analysis system and the blood analysis system according tothe invention will be further elucidated and described with reference tothe drawings, in which:

FIGS. 1A and 1B are schematic diagrams of the beam paths in thedispersive plane and in a plane perpendicular to the dispersive plane,respectively, of an embodiment of the optical analysis system;

FIG. 2 is a schematic diagram of the beam paths in a plane perpendicularto the dispersive plane of another embodiment of the optical analysissystem;

FIG. 3 is a cross-section of an embodiment of the distribution element;

FIG. 4 is a cross-section of another embodiment of the distributionelement;

FIGS. 5A and 5B are schematic diagrams of the beam paths in thedispersive plane and in a plane perpendicular to the dispersive plane,respectively, of another embodiment of the optical analysis system, thebeam paths in the plane perpendicular to the dispersive plane beingunfolded for simplicity; and

FIG. 6 is a schematic diagram of a blood analysis system comprising aspectroscopic analysis system having an optical analysis system.

The Figures are not drawn to scale. In general, identical components aredenoted by the same reference numerals.

DETAILED DESCRIPTION

The optical analysis system 1 for determining an amplitude of aprincipal component of an optical signal, shown in FIGS. 1A and 1B,comprises a dispersive element 2 for spectrally dispersing the opticalsignal. The dispersive element 2 is a grating which spectrally dispersesthe optical signal in a dispersive plane. The beam paths in thisdispersive plane are shown in FIG. 1A, the beam paths in a planeperpendicular to the dispersive plane being shown in FIG. 1B. Instead ofa grating, other dispersive elements such as, e.g., a prism may be used.

The optical analysis system further comprises a focusing member 3 forfocusing the dispersed optical signal. The focusing member 3 has a firstfocal distance in the dispersive plane shown in FIG. 1A and a secondfocal distance in a plane perpendicular to the dispersive plane shown inFIG. 1B. In this embodiment the focusing member 3 is cylinder lens whichfocuses the dispersed optical signal in the dispersive plane, but not inthe plane perpendicular to the dispersive plane. The first focaldistance F₁ is different from the second focal distance F₂ which isinfinite. In alternative embodiments the focusing member 3 is anaspherical lens having two finite focal distances F₁ and F₂.Alternatively, the focusing member may be an aspherical mirror.

The focusing member 3 is arranged to focus the dispersed optical signalin the dispersive plane on the distribution element 4. In the dispersiveplane, rays of different wavelengths are focused on different parts ofthe distribution element 4. In FIGS. 1A and 1B two rays of differentwavelength are depicted by way of example by a dashed line and by adashed double dotted line, respectively.

The distribution element 4 receives the spectrally dispersed opticalsignal and distributes a first part of the optical signal, weighted bythe first spectral weighting function, to a first detector 5 and asecond part of the optical signal, weighted by the second spectralweighting function, to a second detector 6. Embodiments of thedistribution element 4 are shown in FIGS. 3 and 4 and will be discussedbelow. The first detector 5 and the second detector 6 may be any type ofdetector suited to detect light. They may be, e.g., two separatephotodiodes or a split detector.

In the embodiment shown in FIGS. 1A and 1B the optical signal comprisesa principal component having a positive part in a first spectral rangeand a negative part in a second spectral range. A particular ray of awavelength λ₁ of the first spectral range and a particular ray of awavelength λ₂ of the second spectral range are depicted by the dashedline and the dashed double dotted line, respectively. The first part ofthe optical signal weighted by the first spectral weighting functioncorresponds to the positive part and is detected by the first detector5. The second part of the optical signal weighted by the second spectralweighting function corresponds to the negative part and is detected bythe second detector 6. The first detector 5 and the second detector 6are coupled to a signal processor 7 arranged to subtract a signalgenerated by the second detector 6 from a signal generated by the firstdetector 5.

In another embodiment the principal component comprises a firstprincipal component and a second principal component, the first part ofthe optical signal weighted by the first spectral weighting functioncorresponding to the first principal component while the second part ofthe optical signal weighted by the second spectral weighting functioncorresponds to the second principal component. When the first spectralweighting function and the second spectral weighting function do notoverlap, the optical analysis system shown in FIGS. 1A and 1B may beused. However, when the first spectral weighting function and the secondspectral weighting function overlap at least partly, it is required thatthe optical signal of a particular wavelength is partly detected by thefirst detector 5 and partly by the second detector 6. The beam paths inthe dispersive plane may in this embodiment be identical to that shownin FIG. 1A. The beam paths in the plane perpendicular to the dispersiveplane are shown in FIG. 2. The wavelength depicted by the dashed line ispartly detected by the first detector 5 and by the second detector 6.The same holds for the wavelength depicted by the dashed double dottedline. For all wavelengths the relative amounts detected by the twodetectors 5 and 6 are determined by the two spectral weightingfunctions. As will be explained below the distribution element 4 isdesigned to distribute the optical signal to the two detectors 5 and 6accordingly.

In the embodiment shown in FIG. 3, the distribution element 4 is atransparent glass substrate which has a surface 10 for receiving thespectrally dispersed optical signal. The surface 10 comprises a firstset of surface elements 11 and a second set of surface elements 12. Thesurface elements 11 of the first set are arranged to distribute thespectrally dispersed optical signal to the first detector 5,corresponding rays being depicted by a dotted line. The surface elements12 of the second set are arranged to distribute the spectrally dispersedoptical signal to the second detector 6, corresponding rays beingdepicted by a dashed dotted line. In the embodiment of FIG. 3 thesurface elements 11 of the first set are mutually substantially paralleland tilted with respect to the surface elements 12 of the second set,which are mutually substantially parallel as well. This is advantageousin cases where the distribution element 4 is situated substantially inthe focal plane of the focusing member 3. However, it is not essentialaccording to the invention. In an alternative embodiment, not shown, thedistribution element comprises a substrate with a concave and/or convexsurface in which the surface elements are integrated. In this embodimentthe distribution element may be integrated with the focusing member 3 orwith the further focusing member 8.

In FIG. 3 the distribution element 4 is shown in a cross-sectional viewin a plane parallel to the dispersive plane. The part of thedistribution element 4 which is shown enlarged in the upper right partof FIG. 3 receives a first wavelength range of the optical signal.Because the surface elements 11 of the first set and the surfaceelements 12 of the second set have the same surface areas in aprojection perpendicular to the propagation direction of the spectrallydispersed optical signal, 50% of the optical signal in the firstwavelength range is distributed to the first detector 5 and 50% to thesecond detector 6, respectively.

The part of distribution element 4 which is shown enlarged in the lowerright part of FIG. 3 receives a second wavelength range of the opticalsignal. Because of the surface areas of the surface elements 11 and ofthe surface elements 12 seen in a projection perpendicular to thepropagation direction of the spectrally dispersed optical signal, 50% ofthe optical signal in the second wavelength range is distributed to thefirst detector 5 and 25% to the second detector 6, respectively. Thesurface 10 of the distribution element 4 further comprises a third setof surface elements 13 which may direct 25% of the optical signal withthe wavelength of the second spectral component to a third detector orto a beam dump where it is absorbed. In this embodiment the surfaceelements 13 are mutually parallel, but alternatively they may have anyother orientation as long as they do not distribute the optical signalto the first detector 5 or the second detector 6. The surface elements13 may be useful in some cases to satisfy the normalization condition ofthe principal component vector. In this embodiment the first spectralweighting function and the second spectral weighting function aredetermined by the positions and the surface areas of the surfaceelements 11 and the surface elements 12.

In another embodiment, not shown, the distribution element 4 is similarto that shown in FIG. 3, but the spectrally dispersed optical signal isnot refracted as in FIG. 3, but reflected.

The glass substrate shown in FIG. 3 is an optical element which refractsthe spectrally dispersed optical signal because its optical thickness d,i.e. the index of refraction n multiplied by the geometrical thicknesst, d=t n, is a function of the position. Substantially the same patternof the optical thickness d can be obtained in an alternative embodimentas shown in FIG. 4. Instead of a glass substrate the distributionelement 4 comprises an array 20 of liquid crystal elements arranged tocreate substantially the same pattern of the index of refraction n. Tothis end, a first set of sub-arrays 21 having mutually parallelrefractive index gradients and a second set of sub-arrays 22 havingmutually parallel refractive index gradients are formed. The refractiveindex gradients of the first set are tilted with respect to therefractive index gradients of the second set. Analogous to thedistribution element with the surface 10 with surface elements 11 and12, it is not essential that the refractive index gradients are mutuallyparallel. The index of refraction n of each column C is controlled bythe voltage V applied to the cells of the column as is shown in theupper right corner of FIG. 4. The sub-arrays 21 of the first set arearranged to distribute the spectrally dispersed optical signal to thefirst detector 5, corresponding rays being depicted by a dotted line.The sub-arrays 22 of the second set are arranged to distribute thespectrally dispersed optical signal to the second detector 6,corresponding rays being depicted by a dashed dotted line. In thisembodiment the position and the surface area of the sub-arrays 21 and 22of the first set and the second set, respectively, determine the firstspectral weighting function and the second spectral weighting function.

In the embodiment shown in FIGS. 1A, 1B and 2, the optical analysissystem 1 further comprises a further focusing member 8 for focusing thefirst part of the optical signal on the first detector 5. In theembodiment of FIGS. 1A, 1B and 2 the further focusing member 8 is alens. Alternatively or in addition, a focusing mirror may be used.

In the embodiment shown in FIGS. 5A and 5B, the optical analysis system1 further comprises a further dispersive element 9 for spectrallyrecombining the first part of the optical signal prior to focusing thefirst part on the first detector 5. In this embodiment the opticalsignal enters the optical analysis system 1 from a point source 14 whichmay be, e.g., a pinhole in a confocal detection scheme. The opticalanalysis system 1 comprises a lens 15 for collimating the opticalsignal, and a dispersive element 2, being a grating, and a focusingmember 3, being a cylinder lens, analogously to the optical analysissystem 1 shown in the FIGS. 1A, 1B and 2. The focusing member 3 isarranged to focus the dispersed optical signal on the distributionelement 4. In this embodiment the distribution element 4 shown in FIG. 3is arranged to reflect the dispersed optical signal back towards thefocusing member 3 for re-collimation. The re-collimated optical signalis then still spectrally dispersed; this limits the possibility to focusit to a relatively small spot size. To spatially recombine the opticalsignal it is sent to the fixer dispersive element 9 which in thisembodiment is the dispersive element 3, i.e. the dispersive element 3and the further dispersive element 9 are integrated in one grating. Thespectrally recombined optical signal weighted by the first spectralweighting function and the spectrally recombined optical signal weightedby the second spectral weighting function are focused on the firstdetector 5 and the second detector 6 by the lens 15.

In another embodiment, not shown, the distribution element 4 transmitsand refracts the spectrally dispersed optical signal and the furtherdispersive element 9 is arranged to spectrally recombine the opticalsignal weighted by the first spectral weighting function prior tofocusing it on the first detector 5.

The blood analysis system 40 shown in FIG. 6 comprises a spectroscopicanalysis system 30. The spectroscopic analysis system 30 comprises alight source 31 for illuminating a sample 32. The light source 31 maybe, e.g., a light-emitting diode, a lamp or a laser. In this embodimentthe sample 32 is a blood vessel in a finger of a hand. The blood vesselis illuminated by a diode to generate an optical signal having aprincipal component with an amplitude. This optical signal may be, e.g.,a Raman signal having distinct components indicative of distinct bloodcompounds such as, e.g., glucose, lactate, cholesterol, oxy-hemoglobinand/or desoxy-hemoglobin. Each of the compounds has a correspondingprincipal component. To analyze the concentrations of these compounds,the spectroscopic analysis system 30 comprises an optical analysissystem 1 for determining the amplitude of the principal component of theoptical signal as described above.

To determine the concentrations of the compounds, the signals generatedby the first detector 5 and the second detector 6 are further processedby a signal processor 41 of the blood analysis system 40. The signalprocessor 41 has a memory comprising amplitudes of the principalcomponents and the corresponding concentrations of the compounds. Theconcentrations derived from the amplitudes of the principal componentare displayed by a display element 42.

In summary, the optical analysis system 1 is arranged to determine anamplitude of a principal component of an optical signal. The opticalanalysis system 1 comprises a first detector 5 for detecting the opticalsignal weighted by a first spectral weighting function, and a seconddetector 6 for detecting the optical signal weighted by a secondspectral weighting function. For an improved signal-to-noise ratio, theoptical analysis system 1 further comprises a dispersive element 2 forspectrally dispersing the optical signal, and a distribution element 4for receiving the spectrally dispersed optical signal and fordistributing a first part of the optical signal weighted by the firstspectral weighting function to the first detector 5 and a second part ofthe optical signal weighted by the second spectral weighting function tothe second detector 6. The spectroscopic analysis system 30 and theblood analysis system 40 each comprise an optical analysis system 1according to the invention.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of other elements orsteps than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.

The invention has been described with reference to the preferredembodiments. Modifications and alterations may occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be constructed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

1. An optical analysis system for determining an amplitude of aprincipal component of an optical signal, the optical analysis systemcomprising: a first detector for detecting the optical signal weightedby a first spectral weighting function, a second detector for detectingthe optical signal weighted by a second spectral weighting function, adispersive element for spectrally dispersing the optical signal, and adistribution element for receiving the spectrally dispersed opticalsignal and for distributing a first part of the optical signal, weightedby the first spectral weighting function, to the first detector and asecond part of the optical signal, weighted by the second spectralweighting function, to the second detector.
 2. An optical analysissystem as claimed in claim 1, wherein the principal component comprisesa positive part in a first spectral range and a negative part in asecond spectral range, the first part of the optical signal weighted bythe first spectral weighting function corresponding to the positivepart, the second part of the optical signal weighted by the secondspectral weighting function corresponding to the negative part, thefirst detector and the second detector being coupled to a signalprocessor arranged to subtract a signal generated by the second detectorfrom a signal generated by the first detector.
 3. An optical analysissystem as claimed in claim 1, wherein the principal component comprisesa first principal component and a second principal component, the firstpart of the optical signal weighted by the first spectral weightingfunction corresponding to the first principal component, the second partof the optical signal weighted by the second spectral weighting functioncorresponding to the second principal component.
 4. An optical analysissystem as claimed in claim 1, wherein the distribution element has asurface for receiving the spectrally dispersed optical signal, thesurface comprising a first set of surface elements and a second set ofsurface elements, the surface elements of the first set being arrangedto distribute the spectrally dispersed optical signal to the firstdetector, the surface elements of the second set being arranged todistribute the spectrally dispersed optical signal to the seconddetector.
 5. An optical analysis system as claimed in claim 1, whereinthe distribution element comprises an array of liquid crystal elementsarranged to form a first set of sub-arrays having refractive indexgradients, and a second set of sub-arrays having refractive indexgradients, the sub-arrays of the first set being arranged to distributethe spectrally dispersed optical signal to the first detector, thesub-arrays of the second set being arranged to distribute the spectrallydispersed optical signal to the second detector.
 6. An optical analysissystem as claimed in claim 1, wherein the dispersive element is arrangedto disperse the optical signal in a dispersive plane and the opticalanalysis system further comprises a focusing member for focusing thedispersed optical signal, the focusing member having a first focaldistance in the dispersive plane and a second focal distance in a planeperpendicular to the dispersive plane, the first focal distance beingdifferent from the second focal distance.
 7. An optical analysis systemas claimed in claim 6, further comprising a further focusing member forfocusing the first part of the optical signal on the first detector. 8.An optical analysis system as claimed in claim 7, further comprising afurther dispersive element for spectrally recombining the first part ofthe optical signal prior to focusing the first part on the firstdetector.
 9. A spectroscopic analysis system comprising: a light sourcefor illuminating a sample, thereby generating an optical signal having aprincipal component with an amplitude, and an optical analysis systemfor determining the amplitude of the principal component of the opticalsignal as claimed in claim
 1. 10. A blood analysis system comprising aspectroscopic analysis system as claimed in claim 9.